The present invention relates generally to communication receivers and, more specifically, to digital signal processing of analog TV signals in receivers.
There is a demand to provide mobile platforms with the capabilities of viewing TV broadcasting. Although digital TV and HDTV are starting to be deployed, the analog TV broadcasting (NTSC, PAL, etc) has been and is still the most widely available all over the world. Traditionally the analog TV receivers use all analog circuits. For mobile platforms, there is normally a digital signal processor DSP chip available that can be used for different functions such as 3G mobile phone, AM/FM receivers, digital TV receiving, wireless LAN/MAN, etc. The same DSP can also be used to perform the task of analog TV receiving.
The present disclosure is a novel implementation of analog TV receiver on DSP that can allow mobile platforms to view analog TV broadcasting on LCD displays.
The analog television receiver includes a demodulator for demodulating a received analog television signal, an analog to digital converter for digitizing the demodulated television signal and a digital signal processor for producing display signals from the digitized television signals. The digital signal processor being programmed to search for a horizontal synchronization signal in the television signal, track the horizontal synchronization signal and search for a vertical synchronization signal in the television signal. Next the processor separates a luminance and a pair of chrominance components of the television signal and demodulates the pair of chrominance components. Red, green and blue values are constructed from the demodulated chrominance components and the luminance components. Display signals are produced from the red, green and blue values.
The vertical synchronization signal is maintained by using the tracked horizontal synchronization signal. The horizontal synchronization signal may be continuously tracked at least after vertical synchronization has been obtained. The horizontal synchronization signal tracking may include determining an average timing offset and tracking the changes from the average timing offset. The horizontal synchronization signal tracking may be performed by a delay locked loop (DLL). The receiver horizontal synchronization signal tracking should persist for about twenty lines to be valid.
The processor determines scaling gain and DC level from and adjusts the television signals. The phase of the chrominance components are determined and are used in the demodulation of the chrominance components. The phase of the chrominance components may be determined from the color burst asChromaPhase(k)=a tan 2(color_burst_sample(k),color_burst_sample(k+1))These and other aspects of the present disclosure will become apparent from the following detailed description of the disclosure, when considered in conjunction with accompanying drawings.